Muscarinic receptors in the rat ovary are involved in follicular development but not in steroid secretion.

Acetylcholine (ACh) may be involved in the regulation of ovarian functions. A previous systemic study in rats showed that a 4-week, intrabursal local delivery of the ACh-esterase blocker Huperzine-A increased intraovarian ACh levels and changed ovarian follicular development, as evidenced by increased healthy antral follicle numbers and corpora lutea, as well as enhanced fertility. To further characterize the ovarian cholinergic system in the rat, we studied whether innervation may contribute to intraovarian ACh. We explored the cellular distribution of three muscarinic receptors (MRs; M1, M3, and M5), analyzed the involvement of MRs in ovarian steroidogenesis, and examined their roles in ovarian follicular development in normal conditions and in animals exposed to stressful conditions by employing the muscarinic antagonist, atropine. Denervation studies decreased ovarian norepinephrine, but ovarian ACh was not affected, evidencing a local, nonneuronal source of ACh. M1 was located on granulosa cells (GCs), especially in large antral follicles. M5 was associated with the ovarian vascular system and only traces of M3 were found. Ex vivo ovary organo-typic incubations showed that the MR agonist Carbachol did not modify steroid production or expression of steroid biosynthetic enzymes. Intrabursal, in vivo application of atropine (an MR antagonist) for 4 weeks, however, increased atresia of the secondary follicles. The results support the existence of an intraovarian cholinergic system in the rat ovary, located mainly in follicular GCs, which is not involved in steroid production but rather via MRs exerts trophic functions and regulates follicular atresia.

Nerve Growth Factor: A Dual Activator of Noradrenergic and Cholinergic Systems of the Rat Ovary.

The functioning of the ovary is influenced by the autonomic system (sympathetic and cholinergic intraovarian system) which contributes to the regulation of steroid secretion, follicular development, and ovulation. There is no information on the primary signal that activates both systems. The nerve growth factor (NGF) was the first neurotrophic factor found to regulate ovarian noradrenergic neurons and the cholinergic neurons in the central nervous system. The aim of this study was to determine whether NGF is one of the participating neurotrophic factors in the activation of the sympathetic and cholinergic system of the ovary in vivo and its role in follicular development during normal or pathological states. The administration of estradiol valerate (a polycystic ovary [PCO] phenotype model) increased norepinephrine (NE) (through an NGF-dependent mechanism) and acetylcholine (ACh) levels. Intraovarian exposure of rats for 28 days to NGF (by means of an osmotic minipump) increased the expression of tyrosine hydroxylase and acetylcholinesterase (AChE, the enzyme that degrades ACh) without affecting enzyme activity but reduced ovarian ACh levels. In vitro exposure of the ovary to NGF (100 ng/ml for 3 h) increased both choline acetyl transferase and vesicular ACh transporter expression in the ovary, with no effect in ACh level. In vivo NGF led to an anovulatory condition with the appearance of follicular cysts and decreased number of corpora lutea (corresponding to noradrenergic activation). To determine whether the predominance of a NE-induced polycystic condition after NGF is responsible for the PCO phenotype, rats were exposed to an intraovarian administration of carbachol (100 µM), a muscarinic cholinergic agonist not degraded by AChE. Decreased the number of follicular cysts and increased the number of corpora lutea, reinforcing that cholinergic activity of the ovary participates in controlling its functions. Although NGF increased the biosynthetic capacity for ACh, it was not available to act in the ovary. Hence, NGF also regulates the ovarian cholinergic system, implying that NGF is the main regulator of the dual autonomic control. These findings highlight the need for research in the treatment of PCO syndrome by modification of locally produced ACh as an in vivo regulator of follicular development.